The present invention relates to communications switching systems in which redundancy is provided and to a method of providing redundancy in switching systems.
The invention also relates to an access system in which redundancy is provided.
In most systems known today redundancy is provided in different ways to different parts of the system e.g. depending on what is to be provided with redundancy or where in the system redundancy is to be provided. Generally in communications systems the central hardware is duplicated (or even triplicated). For example multiprocessor arrangements are used in which one processor is active whereas the other(s) is/are passive until the operative unit can not operate properly or if an error is detected etc. in which cases a switch is done to one of the standby units. However, further away from the central parts of the switching system redundancy is rarely applied and particularly the access units are not provided with any kind of redundancy at all However, it is known from different systems to make the duplication of arrangements more or less remote from the central parts to a question of costs. Since duplication of equipment considerably increases the costs, redundancy is however often provided only to a limited extent, i.e. to the more central parts of the system
U.S. Pat. No. 4,983,961 describes a non-blocking switching array in three stages. The number of inputs/outputs for the subarrays of its input/output stages is twice the number of lines to be switched and there is one more sub-array in an intermediate stage than what is minimally required to provide a non-blocking switching array The additional inputs/outputs are connected with the non-redundant inputs/outputs so that each redundant input is connected to a non-redundant input of a respective other sub-array of the same stage. If one of the sub-arrays fails, redundant substitute parts are available.
U.S. Pat. No. 5,408,462 discloses a protection switching system comprising a number of telecommunications modules for processing and/or switching telecommunications signals. Signals are provided to a pair of modules by a first module and said pair of modules are in turn connected to a further pair of modules wherein each pair of modules comprises an operating and a stand-by module. The standby module controls the switching of all the modules in the system which require an switching in came the stand-by module is activated and a controller monitor circuit is provided for detecting faults in an operating module in which case the corresponding standby module is informed which then provides the protection switching.
However, none of the today known arrangements works satisfactorily since either there is a risk of loosing data to varying extents upon activating standby equipment or complicated, costly arrangements are provided which however do not provide redundancy throughout the system, i.e. to all parts of the system which means that some parts are totally unprotected which can give serious problems.
Due to the technical progress within the electronical field the packing density of integrated circuits increases continuously. This is the case both as functions or functionalities as such are concerned as well as the number of functionalities of a given kind that can be packed on one and the same physical entity, e.g. a circuit board. A consequence hereof is that in case of mal-functioning of such a unit, the number of users or related systems that are affected increases correspondingly. In order to find a remedy to these problems either smaller physical units than provided for technically would have to be used or redundancy has to be provided in one way or another.
Since it is generally strived at taking advantage of the technological progress and being able to use physical devices that are as small as possible, it is obvious that solutions are preferable which enable the provision of redundancy.
In a communications system the amount of traffic successively increases from the access points or from the access side in direction towards the central parts of the system which means that there is a need of redundancy on a number of different locations.
What is needed is consequently a switching system in which redundancy can be provided in a simple and reliable way and at a low cost.
A system is also needed through which redundancy can be provided also to the parts farther away from the central parts.
A system is also needed which allows the use of physical units with a high or even very high packing density while still keeping the consequences in case of a failure in such a unit very low or even lower as compared to physical units having a lower packing density or generally independently of whether the packing density is high or low although the need for redundancy provision is lower if the physically units are larger and have a low packing density and thus affect fewer users, equipment etc.
A method for providing redundancy is also needed through which it can be done in a simple and reliable way and at a low cost and particularly through which also equipment far away from the central parts can be provided with redundancy in such a manner.
Therefore a communications switching system which comprises a switching network and a number of access units is provided wherein at least a number of multiplexing and switching arrangements which are included in the switching network are so arranged that they form a number of combined multiplexing switching arrangement and wherein a common protection switching arrangement provides protection switching both between access units and multiplexing switching arrangements and between the access units and networks accessing said access units.
In a particular embodiment the control signalling to the access units is effected via the protection switching arrangement and even more particularly the supply of power to the access units by the multiplexing arrangement is effected via the protection switching arrangement. The switching network comprises a number of first switching arrangement and at least one central switching arrangement which is common for a number of access units, in particular all access units of the switching system, wherein the central switching arrangement is a distribution switching arrangement via which all connections to all the access units can reach all the other connections.
According to one embodiment a second protection switching arrangement can be provided for protection switching of the central switching arrangement. This switching arrangement can then be arranged between the combined multiplexing switching arrangements and the central switching arrangement. In general an additional protection switching arrangement can be arranged as a consecutive one following on some switching arrangement that is separately protected.
According to one embodiment the first switching arrangements combined with respective multiplexing arrangements comprise time switches and the central switching arrangement may also comprise a time switch or it may comprise a space switch or any combination thereof.
In one advantageous embodiment, instead of providing separate protection switching of the central switching arrangement, the central switching arrangement is controlled by a number of time switches (first switching arrangements) connected thereto so that the combined multiplexing switching arrangement comprising the corresponding time switches provides redundancy via protection switching on the multiplexing side via the common protection switching arrangement.
In another advantageous embodiment protection switching is also provided to additional equipment which then is connected to the common protection switching arrangement in the same way and on the same side as the combined multiplexing switching arrangements. Alternatively additional equipment can be connected to any second protection switching arrangement in an analogue way.
Particularly protection switching arrangements are introduced on a number of levels in substantially the same way without affecting established connections and in such a way that the same requirements as to transmission speed can be upheld throughout the system so that the whole system is protected in one and the same manner irrespectively of level.
Access can among others be provided to one or more of POTS, ISDN, the asynchronous digital subscriber loop (ADSL) or the high speed subscriber loop (HDSL).
A communications switching system comprising a switching network and a number of access units is also provided wherein the switching network comprises a number of arrangements for multiplexing, switching etc. in which those arrangements between which there is a high speed interface are built together to form combined arrangements which are given redundancy by a common protection switching arrangement. Particularly a number of multiplexing arrangements are built together with a number of switching arrangements, more particularly time switches wherein the common protection switching arrangement is so arranged that it also acts as a protection switch towards the access units. Advantageously m+n redundancy is provided throughout the system wherein m denotes operating arrangements and n denotes redundant arrangements.
Particularly the switching network comprises at least one central distribution switching arrangement wherein a number of time switches connect to the central switching arrangement and protection switching is provided to the distributing switching arrangement via the common switching protection arrangement of the respective combined multiplexing switching arrangements.
An access system for providing communications network access is also provided which comprises a number of access units, multiplexing arrangements and switching arrangements of which one is a central switching arrangement. At least a number of multiplexing arrangements and switching arrangements connecting thereto are combined into a number of multiplexing switching arrangements (units) and a common protection switching arrangement is provided at least for a number of these combined units and it is arranged on the multiplexing side of the said units. The access units are further connected to the common protection switching arrangement so that protection switching is provided in the same way and by the same protection switching arrangement both between the multiplexing arrangements and the access units respectively and between said access units and the accessing networks etc.
The access system may comprise a separate second protection switching arrangement for the central switching arrangement. Alternatively the central switching arrangement is controlled by the time switch arrangements of the switching arrangements (of the combined units) by which it is owned so that protection switching for the distribution switching arrangement is also done via protection switching on the multiplexing side of the combined units. The central switching arrangement particularly comprises a space switch. Alternatively it comprises a combination of time and space switches.
For the same reasons as referred to at the beginning of this section a method of providing redundancy in a switching system of a telecommunications system is provided. The switching system comprises a number of access units and a number of switching arrangements. The method comprises the steps of building together at least some of those arrangements of the switching system which have an interface to another arrangement which is a high transmission speed interface into combined units and introducing protection switching arrangements on different levels of the system in one and the same way irrespectively of which is the level, e.g. for protection of central arrangements of the switching system or accessing units or anything there between so that the requirements as to the transmission speed be the same throughout the system. Advantageously at least a number of multiplexing arrangements are combined with a number of switching arrangements respectively connecting thereto over a high speed interface wherein the switching arrangements for example may be time switches so that they form common units and moreover arranging a common protection switching arrangement for these combined units which provides protection switching both for these combined units and for a number of access units so that the protection switching is handled by the common protection switching arrangement in one and the same way both between multiplexing arrangements and the access units and towards accessing networks.
In an advantageous embodiment controlling of a central switching arrangement of the system such as a distribution switching arrangement is done from the combined multiplexing time switch units owning the switching in the distribution switching arrangement so that protection switching for the distribution switching arrangement likewise is provided by the common protection switching arrangement.